Abstract
Larvae of the rock crab Cancer irroratus Say were hatched and reared under controlled laboratory conditions of temperature and salinity. Zoeae (Stages I–V) and megalopae were exposed to 5 sets of experimental conditions in an experimental column. Variables investigated included darkness, cool-white fluorescent light, and column orientation (horizontal or vertical). Results indicated a positive phototaxis throughout larval development, with the extent of photopositive movement decreasing slightly as metamorphosis to the megalopal stage approached. Conversely, responses to gravity appeared to change significantly as development proceeded, culminating in a rather abrupt and complete transition from geonegative to geopositive behavior in Stage V zoeae. This strong geopositive movement resulted in a change from a planktonic to a benthic habit.
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